According to the 1929 Lateran Treaty, the basilica located in Italian territory is owned by the Holy See and enjoys extraterritorial status similar to that of foreign embassies.[Notes 2] The building is patrolled internally by police agents of Vatican City State, not by Italian police. It is located on Piazza del Esquilino, number 34, some five blocks southwest of the Stazione Termini.

The church is sometimes referred to as Our Lady of the Snows, a name given to it in the Roman Missal from 1568 to 1969 in connection with the liturgical feast of the anniversary of its dedication on 5 August, a feast that was then denominated Dedicatio Sanctae Mariae ad Nives (Dedication of Saint Mary of the Snows). This name for the basilica had become popular in the 14th century[3] in connection with a legend that the 1911 Catholic Encyclopedia reports thus: "During the pontificate of Liberius, the Roman patrician John and his wife, who were without heirs, made a vow to donate their possessions to the Virgin Mary. They prayed that she might make known to them how they were to dispose of their property in her honour. On 5 August, at the height of the Roman summer, snow fell during the night on the summit of the Esquiline Hill. In obedience to a vision of the Virgin Mary which they had the same night, the couple built a basilica in honour of Mary on the very spot which was covered with snow. From the fact that no mention whatever is made of this alleged miracle until a few hundred years later, not even by Sixtus III in his eight-line dedicatory inscription ... it would seem that the legend has no historical basis."[4]

The legend is first reported only after the year 1000.[5] It may be implied in what the Liber Pontificalis, of the early 13th century, says of Pope Liberius: "He built the basilica of his own name (i.e. the Liberian Basilica) near the Macellum of Livia".[6] Its prevalence in the 15th century is shown in the painting of the Miracle of the Snow by Masolino da Panicale.[7][Notes 3]

The feast was originally called Dedicatio Sanctae Mariae (Dedication of Saint Mary's),[4] and was celebrated only in Rome until inserted for the first time into the General Roman Calendar, with ad Nives added to its name, in 1568.[3] A congregation appointed by Pope Benedict XIV in 1741 proposed that the reading of the legend be struck from the Office and that the feast be given its original name.[4] No action was taken on the proposal until 1969, when the reading of the legend was removed and the feast was called In dedicatione Basilicae S. Mariae (Dedication of the Basilica of Saint Mary).[3] The legend is still commemorated by dropping white rose petals from the dome during the celebration of the Mass and Second Vespers of the feast.

The earliest building on the site was the Liberian Basilica or Santa Maria Liberiana, after Pope Liberius (352-366). This name may have originated from the same legend, which recounts that, like John and his wife, Pope Liberius was told in a dream of the forthcoming summer snowfall, went in procession to where it did occur and there marked out the area on which the church was to be built.[8]Liberiana is still included in some versions of the basilica's formal name, and "Liberian Basilica" may be used as a contemporary as well as historical name.[9]

On the other hand, the name "Liberian Basilica" may be independent of the legend, since, according to Pius Parsch, Pope Liberius transformed a palace of the Sicinini family into a church, which was for that reason called the Sicinini Basilica. This building was then replaced under Pope Sixtus III (432-440) by the present structure dedicated to Mary.[8] However, some sources say that the adaptation as a church of a pre-existing building on the site of the present basilica was done in the 420s under Pope Celestine I, the immediate predecessor of Sixtus III.[10]

Long before the earliest traces of the story of the miraculous snow, the church now known as Saint Mary Major was called Saint Mary of the Crib (Sancta Maria ad Praesepe),[11] a name it was given because of its relic of the crib or manger of the Nativity of Jesus Christ, four boards of sycamore wood believed to have been brought to the church, together with a fifth, in the time of Pope Theodore I (640-649).[12][13] This name appears in the Tridentine editions of the Roman Missal as the place for the pope's Mass (the station Mass) on Christmas Night,[14] while the name "Mary Major" appears for the church of the station Mass on Christmas Day.[15]

No Catholic church can be honoured with the title of basilica unless by apostolic grant or from immemorial custom.[16] Saint Mary Major is one of the only four that today hold the title of major basilica. The other three are Saint John Lateran, Saint Peter and Saint Paul outside the Walls.[17] (The title of major basilica was once used more widely, being attached, for instance, to the basilica of Saint Mary of the Angels in Assisi.)[18] All the other Catholic churches that, either by grant of the Pope or by immemorial custom, hold the title of basilica are minor basilicas.

It is agreed that the present church was built under Pope Sixtus III (432-440). The dedicatory inscription on the triumphal arch, Sixtus Episcopus plebi Dei, (Sixtus the bishop to the people of God) is an indication of that Pope's role in the construction.[22] As well as this church on the summit of the Esquiline Hill, Pope Sixtus III is said to have commissioned extensive building projects throughout the city, which were continued by his successor Pope Leo I, the great.[23]

The church retains the core of its original structure, despite several additional construction projects and damage by the earthquake of 1348.

Church building in Rome in this period, as exemplified in Saint Mary Major, was inspired by the idea of Rome being not just the centre of the world of the Roman Empire, as it was seen in the classical period, but the centre of the Christian world.[24]

Santa Maria Maggiore, one of the first churches built in honour of the Virgin Mary, was erected in the immediate aftermath of the Council of Ephesus of 431, which proclaimed Mary Mother of God. Pope Sixtus III built it to commemorate this decision.[25] Certainly, the atmosphere that generated the council gave rise also the mosaics that adorn the interior of the dedication: "whatever the precise connection was between council and church it is clear that the planners of the decoration belong to a period of concentrated debates on nature and status of the Virgin and incarnate Christ."[26] The magnificent mosaics of the nave and triumphal arch, seen as "milestones in the depiction" of the Virgin,[27] depict scenes of her life and that of Christ, but also scenes from the Old Testament: Moses striking the Red Sea, and Egyptians drowning in the Red Sea.

Richard Krautheimer attributes the magnificence of the work also to the abundant revenue accruing to the papacy at the time from land holdings acquired by the Church during the 4th and 5th centuries on the Italian peninsula: "Some of these holdings were locally controlled; the majority as early as the end of the 5th century were administered directly from Rome with great efficiency: a central accounting system was involved in the papal chancery; and a budget was apparently prepared, one part of the income going to the papal administration, another to the needs of the clergy, a third to the maintenance of church buildings, a fourth to charity. These fines enabled the papacy to carry out through the 5th century an ambitious building program, including Santa Maria Maggiore."[28]

Miri Rubin believes that the building of the basilica was influenced also by seeing Mary as a one who could represent the imperial ideals of classical Rome, bringing together the old Rome and the new Christian Rome: "In Rome, the city of martyrs, if no longer of emperors, Mary was a figure that could credibly carry imperial memories and representations."[29]

The basilica was restored, redecorated and extended by various popes, including Eugene III (1145–1153), Nicholas IV (1288–92), Clement X (1670–76), and Benedict XIV (1740–58), who in the 1740s commissioned Ferdinando Fuga to build the present façade and to modify the interior. The interior of the Santa Maria Maggiore underwent a broad renovation encompassing all of its altars between the years 1575 and 1630.

The original architecture of Santa Maria Maggiore was classical and traditionally Roman perhaps to convey the idea that Santa Maria Maggiore represented old imperial Rome as well as its Christian future. As one scholar puts it, “Santa Maria Maggiore so closely resembles a second-century imperial basilica that it has sometimes been thought to have been adapted from a basilica for use as a Christian church. Its plan was based on Hellenistic principles stated by Vitruvius at the time of Augustus.”[30]

Even though Santa Maria Maggiore is immense in its area, it was built to plan. The design of the basilica was a typical one during this time in Rome: “a tall and wide nave; an aisle on either side; and a semicircular apse at the end of the nave.”[24] The key aspect that made Santa Maria Maggiore such a significant cornerstone in church building during the early 5th century were the beautiful mosaics found on the triumphal arch and nave.[citation needed]

The 12th-century façade has been masked by a reconstruction, with a screening loggia, that were added by Pope Benedict XIV in 1743, to designs by Ferdinando Fuga that did not damage the mosaics of the façade. The wing of the canonica (sacristy) to its left and a matching wing to the right (designed by Flaminio Ponzio) give the basilica's front the aspect of a palace facing the Piazza Santa Maria Maggiore. To the right of the Basilica's façade is a memorial representing a column in the form of an up-ended cannon barrel topped with a cross: it was erected by Pope Clement VIII to celebrate the end of the French Wars of Religion.[33]

The mosaics found in Santa Maria Maggiore are not just incredibly beautiful works of Late Antique art; they are also one of the oldest representations of the Virgin Mary in Christian Late Antiquity. As one scholar puts it, “This is well demonstrated by the decoration of Santa Maria Maggiore in Rome,... where the iconographic depiction of the Virgin Mary was chosen at least in part to celebrate the affirmation of Mary as Theotokos (bearer of God) by the third ecumenical Council of Ephesus in 431 CE.”[34] The mosaics of the triumphal arch and the nave in Santa Maria Maggiore were the definition of impressionistic art during the time period and gave a model for the future representations of the Virgin Mary. The influences of these mosaics are rooted in late antique impressionism that could be seen in frescoes, manuscript paintings and many pavement mosaics across villas in Africa, Syria and Sicily during the 5th century.[22]

These mosaics gave historians insight into artistic, religious, and social movements during this time. As one scholar explains that mosaics in Santa Maria Maggiore had two goals: one to glorify the Virgin Mary as Theotokos, (God-Bearer); and the other as the scholar puts is “a systematic and comprehensive articulation of the relationship of the Hebrew Bible and the Christian scriptures as one in which the Hebrew Bible foreshadows Christianity.”[35] This is explained by the dual images of Old Testament and New Testament events depicted in the mosaics of the triumphal arch and the nave. The mosaics also show the range of artistic expertise and refute the theory that mosaic technique during the time was based on copying from model books. The mosaics found in Santa Maria Maggiore are combinations of different styles of mosaic art during the time. As one scholar puts it “the range of artistic expertise and the actual complexities of production can hardly be reduced to a mentality of copying. A test case is given by the mosaics of S. Maria Maggiore in Rome”.[26]

The triumphal arch at the head of the nave was at first referred to as the apse arch, but later became known as the triumphal arch.[36] The triumphal arch is illustrated with magnificent mosaics depicting different scenes of Christ and the Virgin Mary. There was a difference in the styles used in the triumphal arch mosaics compared to those of the nave; the style of the triumphal arch was much more linear and flat as one scholar describes it, not nearly as much action, emotion and movement in them as there were in the Old Testament mosaics of the nave.[26] One of the first scenes that were visible on the triumphal arch was a panel of Christ’s enthronement with a group of angels as his court. As one historian describes it: “On the apse arch Christ is enthroned, a young emperor attended by four chamberlains, angels of course”,[24] this is a perfect example of mosaic art in the 5th century. Another panel found on the triumphal arch is of the Virgin, she is crowned and dressed in a colorful veil, her wardrobe subtly brings to mind that of a Roman empress and in this panel she has her divine son walking with her and a suite of angles and Joseph ready to greet her; “The Virgin...shows to perfection the impressionistic character of mosaics.”[37] Another panel is known as the Adoration of the Magi and this mosaic depicts Infant Christ and The Virgin and the arrival of the three wise men, “mosaics illustrating Christ’s first coming and his youth covered the triumphal arch.”[37] The other panel depicts the Virgin accompanied by five martyrs.[22]

The nave of the basilica was covered in mosaics representing Old Testament events most vividly of Moses leading the Jews out of Egypt across the Red Sea. "The nave mosaics (which represents stories of Old Testament history and accordingly offered Christians in Rome a new 'past') are illusionistic in a colorful and impressionist manner"[26] as this scholar puts it the scene was filled with movement, emotion, and it was to inspire thinking of Rome's "new" past; the past of the Old Testament. The detail used in creating the scene was magnificent as one scholar describes it: "Moses strikes the waters of the Red Sea in a heroic gesture, his toga in light and dark grays and blues, but lined in black, the folds white lines, the tunic underneath light blue; the man next to him wears a deep blue toga over a gray and white tunic."[22] Another panel shows the demise of the Egyptians in the Red Sea. An observer describes the mosaic: "The Egyptians, clad in blue armor with gold bands and scarlet cloaks wildly flying, drown in the greenish blue waters; the horses, white or light brown shaded with darker browns, highlighted in white, the accoutrements a bright red."[37]

Fragments of the sculpture of the Nativity believed to be by 13th-century Arnolfo di Cambio were transferred to beneath the altar of the large Sistine Chapel [38] off the right transept of the church. This chapel of the Blessed Sacrament is named after Pope Sixtus V, and is not to be confused with the Sistine Chapel of the Vatican, named after Pope Sixtus IV. The architect Domenico Fontana designed the chapel, which contains the tombs of Sixtus V himself and of his early patron Pope Pius V. The main altar in the chapel has four gilded bronze angels by Sebastiano Torregiani, holding up the ciborium, which is a model of the chapel itself.

Beneath this altar is the Oratory or Chapel of the Nativity, on whose altar, at that time situated in the Crypt of the Nativity below the main altar of the church itself, Saint Ignatius of Loyola celebrated his first Mass as a priest on 25 December 1538.

The Mannerist interior decoration of the Sistine Chapel was completed (1587–1589) by a large team of artists, directed by Cesare Nebbia and Giovanni Guerra. While the art biographer, Giovanni Baglione allocates specific works to individual artists, recent scholarship finds that the hand of Nebbia drew preliminary sketches for many, if not all, of the frescoes. Baglione also concedes the roles of Nebbia and Guerra could be summarized as "Nebbia drew, and Guerra supervised the teams".

The column in the Piazza Santa Maria Maggiore celebrates the famous icon of the Virgin Mary now enshrined in the Borghese Chapel of the Basilica. It is known as Salus Populi Romani, or Health of the Roman People or Salvation of the Roman People, due to a miracle in which the icon helped keep plague from the city. The icon is at least a thousand years old, and according to a tradition was painted from life by St Luke the Evangelist using the wooden table of the Holy Family in Nazareth.

As a papal basilica, Santa Maria Maggiore is often used by the pope. Most notably, the pope presides over the annual Feast of the Assumption of Mary, celebrated on 15 August each year at the basilica. The canopied high altar is used by the pope alone — except for a few priests including the archpriest. Pope Francis began his first full day as pontiff with a visit to the basilica on 14 March 2013.

^The basilica, which is owned by the Holy See (article 13 of the Lateran Treaty), "form(s) part of the territory of the Italian State (but) enjoy(s) the immunities granted by International Law to the headquarters of the diplomatic agents of foreign States" (article 15 of the Lateran Treaty).

^"Treaty between the Holy See and Italy". Holy See. Article 13: "Italy recognizes the full ownership of the Holy See over the patriarchal Basilicas of St. John Lateran, Sta. Maria Maggiore, and St. Paul, with their annexed buildings. ...
Article 15 The properties indicated in Article 13 hereof ..., even if such edifices form part of the territory of the Italian State, will enjoy the immunities granted by International Law to the headquarters of the diplomatic agents of foreign States."

^This triptych painted around 1423 was commissioned for the basilica by a member of the Colonna family; it is now in the Museo di Capodimonte, Naples (Paul Joannides, "The Colonna Triptych by Masolino and Masaccio," Arte Cristiana no 728 (1988:339-)). The miracle is depicted as witnessed by a crowd of men and women, with Jesus and the Virgin Mary observing from above.

^Archpriest Pietro Sasso is commonly identified with contemporary cardinal Pietro Sasso of S. Pudenziana (1206–1218/19). However, this identification remains uncertain because the only document which mentions this archpriest (dated July 3, 1212) makes no reference to his cardinalate, cf. Ferri in ASRSP, vol. 28, p. 24

^Cardinal Pietro Capocci (died 1259) is mentioned in the majority of the catalogs of archpriests of Liberian Basilica but the documents from the archive of the Basilica, published by Ferri in ASRSP, vol. 27, p. 34–39 and vol. 30, p. 119, give no support for this affirmation. Document dated March 19, 1244 mentions Astor (or Aston) as archpriest, documents between February 13, 1247 and October 1, 1255 mention archpriest without mentioning his name but also without indicating his cardinalate, and on May 28, 1258 Romano was archpriest of the Basilica; the latest document mentions also cardinal Pietro Capocci but makes no reference to his occupation of that post. If he was really an archpriest under Innocent IV, he must have later resigned, but it seems more likely that this statement resulted from a confusion.

^The actual official name seems to vary: The Holy See's press office uses "Papal Liberian Basilica of St. Mary Major in Rome" in English in a 2011 note, while the official Vatican website for the church uses various formulas not including "Liberian" or Liberiana, some under a coat of arms that includes "basilica Liberiana" in Italian.